Re-add calledMain variable using Module[postRun]

`calledMain` global variable was removed from the JS runtime
in emscripten 3.1.17

Author: dmitrylyzo

src/pre-worker.js

@@ -57,6 +57,7 @@ function isBrotliFile(url) {
 Module = Module || {};
 
 Module["preRun"] = Module["preRun"] || [];
+Module["postRun"] = Module["postRun"] || [];
 
 Module["preRun"].push(function () {
     Module["FS_createPath"]("/", "fonts", true, true);
@@ -103,6 +104,12 @@ Module["preRun"].push(function () {
     }
 });
 
+var calledMain = false;
+
+Module["postRun"].push(function () {
+    calledMain = true;
+});
+
 Module['onRuntimeInitialized'] = function () {
     self.octObj = new Module.SubtitleOctopus();